Variable resistances or rheostats are often used in combination with electrical switches, as illustrated in U.S. Pat. No. 4,085,399 in which a resistive element disposed on a circuit board is contacted by a movable wiper. The resistive elements have taken many forms, however a resistive film deposited on the circuit board is often used. An example of such a deposited resistance is disclosed in U.S. Pat. No. 3,921,118 in which the contour of the deposited resistance is shaped to effect a desired resistive function.
The inclusion of a rheostat in a switch intended for automotive application is disclosed in U.S. Pat. No. 3,121,854. There, a switch having an actuator operative in two different modes mechanically effects control of a rheostat through a gearing arrangement associated with the actuator in one mode of control.
More specifically, switches exist for the combined control of a windshield washer and wiper timing, and such switches include provision for adjusting wiper speed through use of a resistance incorporated as part of the switch. Examples of such switches include U.S. Pat. Nos. 2,993,098 and 3,750,080. The U.S. Pat. No. 2,993,098 includes a single discrete resistor mounted on the switch housing and having a single end lead which is fed through for engagement with a movable contact within the switch housing. Such arrangement provides a single intermediate speed.
U.S. Pat. No. 3,750,080 illustrates a switch in which a single actuator element provides two modes of control, one of which includes the provision of a continuous resistive track disposed on a substrate or mounting surface.
In those situations requiring a switch for timed or delay operation of a wiper switch in an automobile, it is now generally desirable to be able to provide at least several wiper sweep delay intervals. Moreover, it is preferable that the switch have substantially repeatable characteristics and that the variable resistance mechanism be free of inconsistencies or unwanted discontinuities. Unfortunately, the direct deposition of a resistive film on the surface of a circuit board does not readily lend itself to an accurate patterning of the film and/or to trimming of the film once deposited. This is particularly true where the desired resistive sequence may be nonlinear in character. Further the deposition of a resistive film or films directly on the circuit board may be troublesome in applications in which the available area for contact wiper scanning on a circuit board must be held to a minimum for compactness of the overall circuit assembly.